1. Field of the Invention
The present invention relates to an element replacement type filter. More particularly, the present invention relates to an element replacement type filter capable of minimizing a required dimension in the radial direction of a casing, and equipped with an anti-loosening mechanism that has a high-strength, highly durable, simple and low-cost construction.
2. Description of the Related Art
Related art is known in which an element replacement type filter is formed by accommodating an element assembly including a filter element within a casing. The casing is formed from a cap and a case, which can be screwed together by relative rotation. Provided between the cap and the case is an anti-loosening mechanism to suppress oil leakage caused by loosening of the cap (see Patent Document 1 for an example).
For example, FIG. 9 shows an anti-loosening mechanism 130 according to known related art, wherein an outer peripheral side of a cap 102 made of synthetic resin is integrally formed with a projecting portion 131, and an outer peripheral side of a case 10 made of synthetic resin is integrally formed with a stopper member 132. The projecting portion 131 is shaped to have a gentle slope in a tightening direction of the cap 102 for easy tightening, whereas a slope in a loosening direction of the cap 102 is sharp so that loosening is difficult.
However, according to the anti-loosening mechanism 130 described above, loosening of the cap 102 is prevented only by the elasticity of the stopper member 132 made of synthetic resin. As a result, the stopper member may be damaged from contact with tools and attachment/removal of the cap under cold conditions, causing problems in terms of strength and durability.
In addition, Patent Document 1 discloses a structure in which a ring-shaped leaf spring that elastically deforms in an axial center direction of the casing is provided on an inner peripheral side of the case. In addition, an inner peripheral side of the cap is provided with concave-shaped portion that can be engaged with a convex-shaped portion of the leaf spring (see FIG. 1 and the like of Patent Document 1 for an example).
Patent Document 1 further discloses a structure in which a mobile pin biased by a coil spring and projectable in the axial center direction of the casing is provided on the inner peripheral side of the case. In addition, a projecting portion that can engage with the mobile pin is provided on the outer peripheral side of the cap (see FIG. 4 and the like of Patent Document 1 for an example).
According to the former structure, however, the anti-loosening mechanism is provided within the casing, which in turn increases the size of an outer periphery dimension of the casing. In particular, use of the ring-shaped leaf spring that elastically deforms in the axial center direction of the case increases the dimension in the radial direction of the casing by at least an amount of space needed to dispose the leaf spring. Moreover, it can be difficult to tell whether the anti-loosening mechanism is defective in any manner.
Also, the anti-loosening mechanism in the latter structure is formed of at least three parts: the mobile pin, the coil spring, and the projecting portion. This results in a complicated and expensive structure with many parts. Furthermore, providing the coil spring and the mobile pin on the outer peripheral side of the cap requires the forming of a projecting portion with a predetermined projection width on the outer peripheral side of the cap, which of course also increases the dimension in the radial direction of the casing. To increase the reliability of the engagement of the mobile pin and the projecting portion in particular, a coil spring whose inner diameter is normally approximately 5 mm is used, and the projecting portion on the outer peripheral side of the cap typically has a projection width of approximately 10 mm. It can be difficult to tell whether the anti-loosening mechanism (especially the coil spring) is defective in any manner. Moreover, there is a risk of problems including reduced slidability of the mobile pin due to the penetration of foreign matter such as sand into the sliding hole of the mobile pin. When such problems occur in the anti-loosening mechanism, the entire cap must be replaced.
[Patent Document 1] Japanese Patent Application Publication No. JP-A-HEI10-249109